1. Field of the Invention
This invention relates, for example, to a video apparatus capable for forming an image area within a display screen displaying a video image having an aspect ratio of 16:9 on a display screen having an aspect ratio of 4:3 or for displaying a video image having an aspect ratio of 4:3 on a display screen having an aspect ratio of 16:9, and a video apparatus having a function of displaying characters, such are letters and symbols, by superimposing them on an image, and particularly to such video apparatus having a function to have a borderline, between a video image area and a non-video image area or a non-image part, which is generated due to deteriorated luminous characteristics of a phosphor of a display element, and characters and symbols on the display hardly recognizable.
2. Description of Related Art
A video display apparatus such as a television receiver using an existing picture tube (cathode-ray tube: CRT) or a video monitor has a display screen having an aspect ratio of 4:3 or 16:9 being a landscape monitor. As information of a video image to be displayed on the display screen, there are video information which shows a circularity 1 when displayed with the aspect ratio of 4:3 (here-in after referred to as a 4:3-image) and video information which shows the circularity 1 when displayed with the aspect ratio of 16:9 (here-in-after referred to as a 16:9-image).
Accordingly, when the video signal is displayed on the display screen having a different aspect ratio from that of the video signal, a circularity becomes other than 1. On this account, conventionally, a size of the video image is changed or a non-video image area is added to a spare space of the video signal in order to make the circularity to be 1 when the video signal is displayed on the display screen having a different aspect ratio.
For example, when the 16:9-image is displayed on a display screen of the aspect ratio of 4:3 in a video display apparatus, only 75% of a video image area Pv is scanned in the vertical direction of the display screen by a deflected electron beam, so that the size of the displayed image is compressed in the vertical direction by 75%, as shown in FIG. 6. Thereby, the circularity in maintained to be 1 and the 16:9-image is correctly displayed.
In this case, a top part and a bottom part of the display screen where the deflected electron beam does not scan becomes a non-video image area Nv where the phosphor does not emit light.
In addition, when the 4:3-image is displayed on the display screen of the aspect ratio of 16:9 in the video display apparatus, only 75% of the video image area Ph in the horizontal direction of the display screen is scanned by the deflected electron beam, so that the size of the displayed image is compressed in the horizontal direction by 75%, as shown in FIG. 8. Thereby, the circularity is maintained to be 1 and the 4:3-image is correctly displayed.
In this case, a left edge and a right edge of the display screen where the deflected electron beam does not scan becomes a non-video image area Nh where the phosphor does not emit light.
In addition, the 16:9-image may be converted into the 4:3-image by adding a non-image part (black band) corresponding to the non-video image area Nv on top or bottom of the 16:9-image and displayed without modification of the size of the video image by the deflection, thereby the image information can be correctly displayed with circularity 1.
In addition, the 4:3-image may be converted into the 16:9-image by adding a non-image part corresponding to the non-video image area Nh on left edge and/or right edge of the 4:3-image and displayed without modification of the size of the video image by the deflection, thereby the image information can be correctly displayed with circularity 1.
Furthermore in a television receiver for receiving television broadcasting, it is broadly done to display characters such as letters and symbols indicating time information, logotypes of the broadcasting program or the like on the video image in superimposing form in order to communicate various information to a viewer.
However, when a time period for displaying video images with compressed image size as shown in FIG. 6 or FIG. 8 becomes long hours, the luminous characteristics of the phosphor of the CRT become different between the video image area Pv and the non-video image area Nv and between the video image area Ph and the non-video image area Nh. Accordingly when the display mode is changed to cancel the size compression of the displayed image, boundary lines between the video image area Pv and the non-video image area Nv and between the video image area Ph and the non-video image area Nh are recognizably left on the display screen of the CRT.
In other words, when the display situation of the CRT is considered, the phosphor of the video image area Pv of the 16:9-image emits light in accordance with the video information, but the phosphor of the non-video image area Nv does not emit light at all as shown in FIG. 6.
Generally, the luminous characteristics of the phosphor is deteriorated if the duration of emitting time of the phosphor becomes long hours, so that the brightness for the video image area Pv of the 16:9-image becomes darker as compared with the brightness of the non-video image area Nv.
When the display mode for displaying the 4:3-image on the display screen having the aspect ratio of 4:3 is selected, the brightness of the video image area Pv, where the 16:9-image is displayed on the display screen having the aspect ratio of 4:3, becomes darker as compared with the brightness of the non-video image area Nv. Furthermore, distinction is recognized in the chrominance levels due to a difference of deteriorated luminous characteristics of the phosphers.
Thereby, a viewer can recognize the boundary lines between the video image area Pv and the non-video image area Nv in the display image of the 16:9-image. In this case, relation between a vertical position of the video image and luminous characteristics of the phosphor is as shown in FIG. 7.
Also in a case of the mode in which the 4:3-image is displayed on the display screen of the aspect ratio of 16:9 as shown in FIG. 8, there is a problem about boundary lines between the video image area Ph and the non-video image area Nh are recognizable.
In addition, in a case where characters and symbols such as logotypes are displayed for a long time in superimposed form on the video image, as the luminous characteristics of the phosphors are different between display positions of the characters and symbols and display positions other than this display positions, so that there is such a problem that display tracks for the characters and symbols are left and recognized by a viewer even after the superimposing display situation is finished.
It is an object of the present invention in consideration of the above points to make it hard to recognize the display tracks of boundary lines between the video image area and the non-video image area caused by the difference of the luminous characteristics deterioration of the phosphor in the display device without giving a sense of discomfort to a viewer.
According to the present invention, when an image is displayed on a display screen having larger display area than the image, a size of the image on the display screen is minutely changed cyclically in order to avoid boundary lines to be recognized when a full size image is displayed on the display screen of the display device. The object of the present invention is to propose such apparatus that has a function to change a size of the image on the display and method therefore.
Namely, according to an aspect of the present invention, there is provided a video display apparatus, which comprises supply means for supplying display signals to a display device; mode control means coupled to the supply means for selecting display modes in the display device between a first display mode where an image having an aspect ratio of 4:3 is displayed on a display screen having the aspect ratio of 4:3 in the display device and a second display mode where an image having an aspect ratio of 16:9 is displayed on the display screen having the aspect ratio of 4:3 in the display device by compressing the image in a vertical direction; and size change means coupled to the supply means for changing minutely and cyclically a size of a display image displayed on the display device in the vertical direction in the second display mode.
According to the first aspect of the present invention, in a case where the second mode is selected, since the display size of the 16:9-image is changed minutely and cyclically in a vertical direction, difference in deterioration of luminous characteristics of the video image area and the non-video image area at the boundary line becomes not significant due to the slight size reduction so that it is not recognizable and does not five a sense of discomfort to a viewer.
Further, in a second aspect of the present invention, there is provided a video display apparatus, which comprises: supply means for supplying display signals to a display device; mode control means coupled to the supply means for selecting display modes in the display device between a first mode where an image having an aspect ratio of 4:3 is displayed on a display screen of the display device having an aspect ratio of 4:3 and a second mode where an image having an aspect ratio of 16:9 is displayed on the display screen of the display device with additional non-image part on top and bottom of the displayed image having an aspect ratio of 16:9; and size change means coupled to the supply means for changing minutely and cyclically a size of the image displayed on the display device in the vertical direction.
According to the second aspect of the present invention, in a case where the second mode is selected, since the display size of whole displayed image is changed minutely and cyclically in a vertical direction, difference in deterioration of luminous characteristics of the video image area of the aspect ratio of 16:9 and the non-image part at the boundary line becomes not significant due to the slight size reduction so that it is not recognizable and does not five a sense of discomfort to a viewer.
In a third aspect of the present invention, there is provided a video display apparatus, which comprises: supply means for supplying display signals to a display device; mode control means coupled to the supply means for selecting display modes in the display device between a first display mode where an image having an aspect ratio of 16:9 is displayed on a display screen having the aspect ratio of 16:9 in the display device and a second display mode where an image having an aspect ratio of 4:3 is displayed on the display screen having the aspect ratio of 16:9 of the display device by compressing the image in a horizontal direction; and size change means coupled to the supply means for changing minutely and cyclically a size of a display image displayed on the display device in the horizontal direction in the second display mode.
According to the third aspect of the present invention, in a case where the second mode is selected, since the size of display image of the aspect ratio of 4:3 is changed minutely and cyclically in a horizontal direction, difference in deterioration of luminous characteristics of the video image area and the non-video image area at the boundary line becomes not significant due to the slight size reduction so that it is not recognizable and does not five a sense of discomfort to a viewer.
A fourth aspect of the present invention provides a video display apparatus, which comprises supply means for supplying display signals to a display device; mode control means coupled to the supply means for selecting display modes in the display device between a first mode where an image having an aspect ratio of 16:9 is displayed on a display screen of the display device having an aspect ratio of 16:9 and a second mode where an image having an aspect ratio of 4:3 is displayed on the display screen having the aspect ratio of 16:9 of the display device with additional non-image part on a left edge and a right edge of an displayed image having the aspect ratio of 4:3; and size change means coupled to the supply means for changing minutely and cyclically a size of the display image displayed on the display device in a horizontal direction.
According to the fourth aspect of the present invention, in a case where the second mode is selected, since the size of whole display image is changed minutely and cyclically in a horizontal direction, difference in deterioration of luminous characteristics of the video image area of the aspect ratio of 16:9 and the non-image part at the boundary line becomes not significant due to the slight size reduction so that it is not recognizable and does not five a sense of discomfort to a viewer.
A fifth aspect of the present invention provides a video display apparatus, which comprises: character generating means for generating characters and symbols; supply means for supplying display signals to a display device for displaying an image on which the signals form the character generating means are superimposed; and size change means coupled to the supply means for changing minutely and cyclically a size of a displayed image displayed on the display device in a horizontal direction and/or a vertical direction.
According to the fifth aspect of the present invention, with regard to the image on which characters and symbols are superimposed, since the size of whole display image is changed minutely and cyclically in a vertical direction or a horizontal direction, difference in deterioration of luminous characteristics of characters and symbols becomes not significant due to the slight size reduction so that display tracks of the characters and symbols are hardly recognizable and does not five a sense of discomfort to a viewer.
The present invention is also related to a method for displaying an image, the method comprises the steps of: determining a mode to be selected from a first mode where an image having an aspect ratio of 4:3 is displayed on a display screen having the aspect ratio of 4:3 and a second mode where an image having an aspect ratio of 16:9 is displayed on the display screen having the aspect ratio of 4:3; compressing a size of an image displayed on the display screen in a vertical direction to have the aspect ratio of 16:9 in a case where the second mode is selected; and changing minutely and cyclically a size of the image compressed to have the aspect ratio of 16:9 in the vertical direction.
Further, this invention relates to a method for displaying an image, comprising the steps of: determining a mode to be selected from a first mode where an image having an aspect ratio of 16:9 is displayed on a display screen having the aspect ratio of 16:9 and a second mode where an image having an aspect ratio of 4:3 is displayed on the display screen having the aspect ratio of 16:9; compressing a size of an image displayed on the display screen in a horizontal direction to have the aspect ratio of 4:3 in a case where the second mode is selected; and changing minutely and cyclically a size of the image compressed to have the aspect ratio of 4:3 in the horizontal direction.
In another aspect of the present invention, there is provided a method for displaying an image, in which a size of a display image is changed minutely and cyclically in a vertical direction and/or horizontal direction in a case where characters and symbols are superimposed on the display image.